The present invention relates to a sputtering target, in particular, a carbon (C) particle-dispersed Fe—Pt-based sputtering target, for producing thermally assisted magnetic recording media.
In the field of magnetic recording represented by hard disk drives, ferromagnetic metal-based materials, i.e., Co, Fe, or Ni-based materials, are used as materials of magnetic thin films in magnetic recording media. For example, in the magnetic thin film of a hard disk employing a longitudinal magnetic recording system, a Co—Cr-based or Co—Cr—Pt-based ferromagnetic alloy mainly composed of Co has been used.
In magnetic thin films of hard disks employing a perpendicular magnetic recording system, which has been recently applied to practical use, composite materials each composed of a Co—Cr—Pt-based ferromagnetic alloy mainly composed of Co and nonmagnetic inorganic particles are widely used. In many cases, the magnetic thin film is produced by sputtering a sputtering target made of the above-mentioned materials with a DC magnetron sputtering apparatus because of its high productivity.
Incidentally, the recording density of a hard disk is rapidly increasing year by year, and it is predicted that the areal recording density will reach 1 Tbit/in2 in the future, whereas the current areal recording density is 600 Gbit/in2. In order to achieve a recording density of 1 Tbit/in2, the recording bit size must be reduced to nm or less. In such a case, occurrence of a problem of superparamagnetization due to thermal fluctuation is predicted. The magnetic recording medium materials currently used, e.g., Co—Cr-based alloys having enhanced crystal magnetic anisotropy by containing Pt therein, are predicted to be insufficient for preventing the problem, and magnetic particles that behave as a stable ferromagnetic material in a size of 10 nm or less need to have higher crystal magnetic anisotropy.
Based on the above-described circumstances, an Fe—Pt phase having a L10 structure has attracted attention as a material for ultra-high density recording media. The Fe—Pt phase having a L10 structure has not only high crystal magnetic anisotropy but also excellent corrosion resistance and oxidation resistance and is therefore expected as a material that is suitable to be applied to magnetic recording media.
In order to use the Fe—Pt phase as a material for an ultra-high density recording medium, it is necessary to develop a technology of dispersing Fe—Pt magnetic particles regulated in the same direction with a density as high as possible in a magnetically isolated state.
Accordingly, a magnetic thin film having a granular structure in which Fe—Pt magnetic particles having a L10 structure are isolated from one another by a nonmagnetic material such as an oxide or carbon has been proposed as a magnetic film for a magnetic recording medium of the next-generation hard disk employing a thermally assisted magnetic recording system.
The granular magnetic thin film has a structure in which the magnetic particles are magnetically isolated from one another by means of the intervention of a nonmagnetic material.
Magnetic recording media including magnetic thin films having a granular structure are described in literatures such as Patent Literatures 1 to 5.
Among the granular magnetic thin films including an Fe—Pt phase having the L10 structure, a magnetic thin film containing 10% to 50% by volume of carbon as a nonmagnetic material has particularly attracted attention from its high magnetic characteristics. Such a granular magnetic thin film is known to be produced by simultaneously sputtering an Fe target, a Pt target, and a C target or simultaneously sputtering an Fe—Pt alloy target and a C target. In order to simultaneously sputtering these sputtering targets, however, an expensive co-sputtering apparatus is necessary.
In general, sputtering of a sputtering target containing a nonmagnetic material in a form of an alloy with a sputtering apparatus has problems of causing unintended detachment of the nonmagnetic material during the sputtering or generation of particles (dust adhered to a substrate) due to abnormal discharge occurring from holes present in the sputtering target. In order to solve these problems, it is necessary to enhance the adhesion between the nonmagnetic material and the base alloy and to increase the density of the sputtering target. In general, the sputtering target material containing a nonmagnetic material in a form of an alloy is produced by a powder sintering method. However, in the case of an Fe—Pt alloy containing a large amount of C, since C is a material which is not susceptible to be sintered, preparation of a sintered compact having a high density is difficult.
As described above, a Co—Cr—Pt alloy has been widely used as the magnetic phase of a perpendicular magnetic recording layer until now. However, an increase in the recording density needs a reduction of the Co alloy size per bit and also causes a problem of superparamagnetization due to thermal fluctuation. Accordingly, Fe—Pt having a high crystal magnetic anisotropy is attracting attention.
Furthermore, in general, a magnetic recording layer is composed of a magnetic phase of, for example, Fe—Pt and a nonmagnetic phase isolating the magnetic phase, and carbon is known to be effective as a nonmagnetic phase.
However, carbon is a material which C is a material which is not susceptible to be sintered and is susceptible to form aggregates and therefore has problems of readily causing detachment of carbon lumps occurs during sputtering to result in generation of a large number of particles on the film after sputtering.
Accordingly, though improvement of magnetic recording layers has been tried by introducing carbon into a target, the problems in sputtering of the target has not been solved yet.
In addition, formation of a carbon film is proposed. For example, Patent Literature 6 describes:
a magnetic disk including an amorphous hydrogenated carbon layer having one wave peak (A) at a position of 1545 cm−1 or less and another wave peak (B) at a position of 1320 to 1360 cm−1 and having an area ratio (B/A) of these waves at the half-value widths of the peaks in 0.3 to 0.7, and a method of producing the magnetic disk.
Patent Literature 7 describes a method of evaluating a carbon film including a step of evaluating the film quality of the carbon film based on the ratio ID/IG of the intensity ID of a band D (disorder) having a peak at about 1350 to 1450 cm−1 to the intensity IG of a band G (graphite) having a peak at about 1550 to 1650 cm−1 in a surface-enhanced Raman spectrum and a step of confirming whether the ID/ID is in the range of 0.1 to 0.5, and a method of producing a magnetic recording medium.
The methods described in Patent Literatures 6 and 7 are, however, merely evaluation of carbon films and do not directly relate to the influence of carbon on a sputtering target when a large amount of carbon is present in the magnetic metal that is a main constituent material of the target for forming a magnetic recording film, the behavior of carbon in the step of producing the target, and the influence on formation of a film by sputtering using the target. Thus, these methods are not technologies in which these influence and behavior are sufficiently revealed.
Patent Literatures 8 and 9 describe evaluation of a SiC- or C-based thin film of a magnetic recording medium by a Raman spectrum and do not directly relate to the influence of carbon on a sputtering target when a large amount of carbon is present in the magnetic metal that is a main constituent material of the target for forming a magnetic recording film, the behavior of carbon in the step of producing the target, and the influence on formation of a film by sputtering using the target. Thus, these methods are not technologies in which these influence and behavior are sufficiently revealed.